Rudy, a 10-year-old neutered male Border collie, presented for evaluation of pruritic skin lesions that had erupted over the previous month. Rudy had a history of epilepsy that was well-controlled with phenobarbital. In addition to the skin lesions, Rudy’s owners had noticed that he was reluctant to go for his daily walks, was extremely lethargic, and could no longer hold himself upright on slick surfaces. On physical examination, the skin lesions consisted of several erythemic papules, plaques, and nodules that were firm in nature (see photo). The largest plaques were present on the dorsal head and dorsal neck. Rudy’s blood work revealed elevated liver enzyme activities, and the findings of an ultrasonographiic examination of his abdomen were unremarkable with the exception of hepatomegaly.
What condition do the skin lesions most likely represent?